[Jayce]

Try a painted sheild one that wont get chassis ground

Hmmm. That could work or a rubber strip between the shield and the chassis. Just odd that it acts up with the shield on and plays fine with it off. I thought maybe the shield was bent and making contact with the top connectors on the 24s (they are rather high set), but that doesn't seem to be the issue. The screw holes are slotted for adjustmet up and down, so might fiddle with that.